Process for heat treating plasma-consolidated beryllium

ABSTRACT

A three stage process for heat treating plasma-consolidated beryllium to produce highly densified beryllium having a theoretical density greater than 99 percent.

Unite States Patent [191 Taylor et al.

1451 Feb. 12, 1974 PROCESS FOR HEAT TREATING PLASMA-CONSOLIDATEDBERYLLIUM [75] Inventors: Thomas A. Taylor; Robert J. Baird,

both of Indianapolis, Ind.

[73] Assignee: Union Carbide Corporation, New

York, NY.

[22] Filed: Sept. 28, 1970 [21] Appl. No.: 76,258

[52] US. Cl 117/93.1 PF, 75/200, 75/227, 117/105.2, 117/1 19.6, 264/60,264/66 [51] Int. Cl 805k 7/22 [58] Field of Searchl 17/93.1 PF, 105,105.1, 105.2,

3,115,408 12/1963 Knight 75/200 3,305,358 2/1967 Lirones i 75/2113,576,932 4/1971 Biddulph 264/65 3,053,610 9/1962 Shichman 117/1053,532,493 10/1970 Chay 75/227 OTHER PUBLICATIONS Foos et al.,MicroAlloying Relationships in Beryllium from National Material AdvisorBoard, publication NMAB-272, July 1970.

Primary ExaminerAlfred L. Leavitt Assistant Examiner-John H. NewsomeAttorney, Agent, or Firm-James C. Arvantes; Harrie M. Humphreys; RobertC. Cummings [57] ABSTRACT A three stage process for heat treatingplasmaconsolidated beryllium to produce highly densifled berylliumhaving a theoretical density greater than 99 percent.

10 Claims, No Drawings PROCESS FOR HEAT TREATING PLASMA-CONSOLTDATEDBERYLLIUM 1. Field Of The Invention This invention relates to a processfor heat treating 5 plasma-deposited beryllium so as to produce a highlydensified substantially isotropic polycrystal beryllium article havingexcellent mechanical and physical properties. The process comprisesessentially a three-stage procedure whereby the plasma-depositedberyllium is first subjected to a temperature controlled outgassingdesorption stage, followed by a temperature controlled sintering stagefor densifying the beryllium article and then concluding with atemperature regulated cooling stage to control the impurity distributionin the beryllium through solution and/or precipitation reactions.

2. Description Of The Prior Art Beryllium offers a combination of lowdensity and high strength which make it a desirable product for use asan aerospace structural material. In addition, its thermal and hardeningproperties makes it attractive as a heat sink and thus qualifies it foruse as a skin covering for aerodynamical vehicles. The large thin-wallshapes required for aerodynamic applications are difficult to fabricateand are quite expensive to produce. it is common practice to first forgeor hot-press a large block of beryllium and then machine it to provide adesired smaller-shaped article. The expense incurred in the machiningoperation plus the waste of the scraps therefrom results in an expensivefinish product. .Another method of fabricating beryllium shaped articlesis to first produce beryllium sheets and then form the sheets to theparticular shape desired. This method of fabrication not only producesan unattractive article but also an expensive one since the sheetsusually have to be joined thereby requiring an additional costlyoperational step.

A significant advancement in the fabrication of unitary thin-wallberyllium shapes has recently been devised by using the plasma arc-torchcoating technique described in U.S. Pat. Nos. 2,858,411 and 3,016,447.Basically plasma arc coating is a method for continually depositing apowder coating material on the surface of a workpiece. An electric arebetween a nonconsumable stick electrode and a spaced apart secondelectrode is provided whereupon a stream of gas is then passed incontact with the stick electrode to be contained therein thus forming anarc-containing gas stream. A portion of the gas stream iswall-stabilized so as to collimate the energy of the arc thus providinga high thermal content effluent. Coating material, such as beryllium inthe powder form, is then passed into the stream whereupon the heat ofthe high thermal content effluent melts and propels the coating materialonto the workpiece thereby resulting in an evenly applied, fine grainsize coating on the workpiece. This coating process is continued until auniform layer of the precise thickness is deposited on the workpiece.Thus various shapes can be fabricated quickly and economically. Thedrawback with this fabrication technique, however, is that it results ina plasma-consolidated end product having less than full theoreticaldensity and relatively poor mechanical properties thus limiting its useto applications where density and strength are not critical.

SUMMARY OF THE INVENTION The present invention is directed to a processfor heat treating as-coated plasma-consolidated beryllium articles so asto convert them to high density beryllium articles having greatlyincreased strength and ductility.

Specifically, a plasma-consolidated, pre-shaped beryllium article isfirst prepared using the plasma arc- 0 torch coating technique. Thespecific size of the beryllium powder to be used in the plasma arc-torchprocess to prepare the beryllium article is somewhat important since thecoating efficiency of the process and the articles mechanical propertiesof strength and ductility are somewhat dependent upon the powder size ofthe coating material, i.e. powder size between 10 microns and 50 micronswill provide optimum coating efficiency and higher mechanical propertiesfor the coated article. From experimentation it has been found that apowder size of 325 Tyler mesh (44 microns) and finer provides a goodefficient coating process while yielding a consolidated layer ofberyllium having good mechanical properties. However, with the design oflarger powered arc torches than are commercially available today, it maybe possible to increase the size of the beryllium powder to be usedsince a larger size are would produce more heat which could effectivelymelt larger size powder particles prior to propelling them onto theworkpiece.

Another variation in the as-coated plasma consolidated beryllium articleto be evaluated is the density of the article with reference to a 100percent theoretical density corrected for BeO contents according to theformula BeO 1.8477 3.009

Densities between 78 and 93 percent theoretical have been found inas-coated beryllium samples and using the beryllium samples with densityvalues near this lower density range, it was found that it was difficultand even impossible to increase the density value of the articleaccording to the heat treating process of this invention to above 99percent theoretical without excessively increasing the grain growth inthe final product. Thus a density greater than 85 percent theoreticaland preferably greater than 87 percent theoretical have been found to berequired in utilizing the process of this invention to produce an endproduct with a'density greater than 99 percent theoretical withoutunduly increasing the grain size of the product.

A third variation to be considered before subjecting the as-coatedplasma-consolidated beryllium article to the heat treating process ofthis invention, is its oxygen contents expressed as the percentage ofBeO by weight of the article. At higher oxide levels, not only is thestrength and elastic modulus properties enhanced but also the sinteredgrain size is decreased. A BeO percentage, by weight of the beryllium,of between about 1.5 and about 2.5 percent, and preferably about 2.0percent, is desirable for use with this process in obtaining adensified, high strength end product, although a BeO content up to 6percent can produce a high density usable beryllium product. Forexample, an as- 3 coated article with 1.7 percent BeO yields a berylliumproduct, after the heat treating process of this invention, having agrain size of 18 microns and a tensile strength at 26C of 40,625 poundsper square inch while a similar as-coated article with 2.2 percent BeOyields a product having a grain size of 6 microns and at 26C, a tensilestrength of 56,264 pounds per square inch. Thus by selecting the Ecocontents in the ascoated article, the grain size and mechanicalproperties of the final product can be controlled. The exact percentageof BeO can be adjusted through the plasmaconsolidation process, that is,the particular are torch used, the particular beryllium powder employedand the size and intensity of the arc developed during the plasmaspraying operation.

By selectively electing the desired values of the above-specifiedvariables and then subjecting the plasma-consolidated beryllium articleto the timetemperature profile of the heat treatment of this invention,a highly densified, substantially isotropic polycrystal berylliumarticle having excellent ductility and strength properties can beproduced. Thus prior to initiating the heat treatment of this invention,the ascoated plasma consolidated articles should have a density greaterthan 85 percent theoretical and a BeO content of up to 6 percent andpreferably between about 1.5 and about 2.5 percent by weight.

A substantially isotropic polycrystal beryllium article is intended tomean an article having orientation factors 1 equal to no higher than 0.2and defined as where D equals the orientation factor for X-rayreflection j measured on face i of a cubical specimen havingorthogonally disposed faces.

i the subscript denoting the particular face of the specimen underexamination (i l, 2 or 3).

jthe subscript denoting the specific X-ray reflection from the followingplanes of the specimen:

101 0, 0002, l l l, 1120, T3 and 1122.

1 equal the integrated X-ray intensity from face i for a specificreflection, j.

1, equals the average integrated X-ray intensity determined from threefaces of a cubical specimen for a specific reflection j. Thus byexamining the crystallographic texture of a beryllium article by X-raydiffraction means, the exact grain orientation factor of the article caneasily be calculated and when the article is heat treated according tothis invention, it will have an orientation factor of 0.2 or lessaccording to the above formulas.

High density is intended to mean a density of greater than 99 percenttheoretical based on a 100 percent theoretical density for berylliumcorrected for BeO contents according to the formula Theoretical densitywggfiyflgeo The first stage of the heat treating process according tothis invention is initiated by placing an as-coated plasma-consolidatedberyllium article having a theoretical density greater than 85 percentand BeO contents up to 6 percent and preferably between about 1.5 andabout 2.5 percent by weight, into a substantial vacuum and controllablyheating the article to outgas and/or thermally desorb the contaminentsoccupying the pores and pore surfaces of the article, such as gases andcondensed gases, respectively. The source of some of these contaminentscan be attributed to normal air (nitrogen and oxygen), arc-torch gas(mainly argon), substrate coolant (mainly CO and adsorbed moisture (H O)since these contaminents are usually present in all plasma-consolidatedcoatings. The article during this outgassing desorption stage can beheated at a rate and for a time period necessary to reduce the typicalas-coated adsorbed gas level of approximately 10' moles per cubiccentimeter of porosity or void to at least 10 moles per cubic centimeterof porosity and preferably to 10' moles per cubic centimeter ofporosity. However, the temperature has to remain below the temperaturewhere the internal porosity is closed off from the surface throughevaporation-condensation and densitication shrinkage mechanisms. Thisupper temperature level referred to as the sintering start temperature,is a function of the density of the as-coated beryllium article and canbe as low as 600C for as-coated articles having a 90 percent theoreticaldensity whereas an ascoated article having an 85 percent theoreticaldensity requires a temperature of about 700C to commence internalporosity closure. Generally this outgassing desorption stage can besuccessfully implemented by placing the article in a vacuum of less than10 torr and then subjecting it to a time-temperature heating profile ofless than 10C per minute and preferably about 4C per minute. Anotherheating procedure is to rapidly heat the article in a substantial vacuumto about 500C and then holding thereat for at least 30 minutes to insurethat the level of contaminents has decreased to a tolerable level ofless than 10 moles per cubic centimeter of porosity.

The substantially outgassed article is then subject to a heating stagewhereby the temperature is increased to a level where full densificationof the article will occur, such temperature being the sinteringtemperature and being at least l,lC. The article is then held at thistemperature until a density of greater than 99 percent theoretical isobtained. The time period for maintaining the article in this hightemperature environment is somewhat limited since prolonged exposure tohigh temperature will increase the grain size of the article and therebydecrease its mechanical properties. In general, heating the outgassedarticle to a temperature between at least l,l80C and about l,250C for aperiod of between about 15 minutes and about 6 hours will be sufficientto successfully densify the article to above 99 percent theoreticalwithout substantially increasing the grain size of the article.Preferably heating the outgassed article to 1,200C 10C for a period of3.5 hours i 0.5 hours will be sufficient to produce an excellentdensified beryllium article based on initial ascoated beryllium articlehaving a density greater than percent theoretical and a BeO contentpreferably between about 1.5 and about 2.5 percent by weight. Thisdensification stage of the process should be carried out in an enclosedheated zone slightly larger than the beryllium article so as to minimizethe overall evaporation loss of the beryllium. The exact ratio of volumeof the heated zone to surface area of the article is not critical to theprocess but a ratio of not greater than 1.0 inch is preferred.

The highly densified beryllium article is then subjected to the thirdand final stage of the heat treating process whereby it is controllablycooled at a rate sufficient to control the impurity distribution withinthe article by solution and/or precipitation reactions to produce astrong and ductile beryllium article. Commercially available berylliumis actually a multi-phase alloy since impurities contained therein, suchas aluminum and silicon, have extremely low solubility and are forced toreside mainly at the grain boundaries. For example, at temperatureswithin the range of 400C to 700C, aluminum and silicon eutectics withberyllium can form thereby resulting in loss of ductility to thearticle. However, aluminum can react with the impurity iron andberyllium to form a refractive intermetallic which can restore any lossof ductility to the article. Thus a time-temperature cooling profilefollowing the densification stage of the process is required to produceand distribute within the article at least one of the berylliumcompounds in the group consisting of Al- FeBe,, AlFeBe FeBe FeBe andsimilar compounds with substitution of silicon and other transitionmetal elements, so that the physical properties of the article will notbe substantially reduced. For example, by reacting free aluminum orsilicon with iron and beryllium to form compounds of the general typeAlFeBe we can avoid having free aluminum and silicon at the grainboundaries where they could decrease the ductility of the berylliumarticle.

A cooling rate of between about 1C and about C per minute is sufficientto substantially control the impurity distribution within the berylliumarticle during this final stage of the process to produce a verydesirable finished product. Preferably a cooling rate of between about1.5C and about 2C per minute is desirable. It is also possible torapidly cool down the article to a temperature between about 500C andabout 750C and then age or hold the article thereat for a period of atleast 10 hours to produce the desired solution and/or precipitationreactions.

Where it is required that there be no extraordinary ductility loss attemperatures of about 500C, then an additional aging step will becomenecessary whereby the article is maintained, after the substantialimpurity distribution stage, at a temperature of between about 500C andabout 750C for a time period between about 10 hours and about 100 hours.

The exact time-temperature profile of the heat treating process of thisinvention to be used for any particular shaped article depends on theinitial properties of the as-coated plasma-consolidated berylliumarticle including its impurity contents. In addition, the temperaturerange and time duration for each stage of this process will also be afunction of the properties desired in the finished product which isusually dictated by its intended applicational use.

EXAMPLE 1 325 Tyler Mesh and finer Argon Argon-Hydrogen 150-200 amperesPowder size Electrode Gas Powder Carrier Gas Current of Arc Torch-Continued Voltage of Arc Torch 55-70 volts Torch Pressure 29-34 psigDispenser Pressure 36-39 psig Shield None Coating Time 7 Hr. 55 MinutesCoating Thickness 0.500 inch Powder Feed Rate Anode Type Torch Standoff13 grams per minute Copper Anode 1.5 inches The chemical analysis of theberyllium powder was as follows:

% Be 98.48 BeO 1.10 Al 0.06 C 0.14 Fe 0.15 Mg 0.02 Si 0.05

The plated article was a flat disc measuring 0.5 inch thck and 19 inchesin diameter. The as-plated density, measured by standardwater-displacement method as described in ASTM Designation B 328-60,1968 Book of ASTM Standards, Part 7, Page 440, was 1.59 grams per cubiccentimeter. The oxygen content was determined by neutron activation tobe 2.2 percent as BeO. The as-coated density, corrected for oxygencontent, was 85.5 percent of theoretical.

The disc was cut into approximately 5 X 5 inch plates and enclosed in atight-fitting box of graphite, coated in the inside with a BeO reactionbarrier. The box was evacuated to 10 torr and heated to 800C at 4C perminute. At this point the furnace chamber was backfilled with argon atmicrons of pressure and then the heating continued at 4C per minuteuntil reaching 1,200 to 1,205C where the sample was held for four hours.Cooling to room temperature was then commenced under the same argonatmosphere at a cooling rate of 1.7C per minute.

Specimens were cut from this sintered plate and measured for density.Based on 2.2 percent BeO (asanalyzed), the heat treated density was 100percent theoretical, corrected for BeO content. The heat treated grainsize by the linear intercept method gave a 6 microns average. The barswere then machined to the tensile specimen configuration of ASTM-E8,using a Tensile-Grind contouring machine. Each specimen was handpolished down to 400 grit SiC abrasive paper, then electrochemicallyetched to remove 0.002 0.003 inch per side. The etching conditions weresolution: 60% phosphoric acid 35% glycerine 5% of 50% Chromic acidsolution voltage: 18-20 temperature: 60-80C with stirring of solutionand agitation of the specimen TABLE 1 Elevated Temperature TensileProperties Bar A As-densified condition (no aging or stress relieving)Strain rate: 0.004 in/in/min T, "C YS (psi) 0.2 UTS (psi) Ultimate E,,(elongation) As-densified" condition (no aging or stress relieving)Strain rate: .08 in/inlmin T, "C YS (psi) 0.2 UTS (psi) 12,, 100 45,98056,667 3.55 300 49,333 50,111 3.74 400 42,340 44,681 14.69 500 31,98240,090 10.02 600 26,636 22,626 14.08 700 13,119 13,486 10.16

Bar C Aged 12 hr. at 600C Strain rate: 0.004 in/in/min T, C YS (psi) 0.2UTS (psi) 5,, 26 47,776 57,021 2.08 300 36,022 41,935 14.8 500 27,41933,011 10.36 700 7,312 7,419 2.76

Bar D Aged 100 hr. at 600C Strain rate: 0.004 in/in/min 26 49,247 61,2902.4 300 35,444 45,556 18.91 500 28,587 32,174 9.12 700 8,851 9,195 2.66

Bar E Aged 200 hr. at 600C Strain rate: 0.004 in/in/min 26 42,935 51,5220.98 300 33,542 44,896 14.89 500 26,559 29,140 8.34 700 6,947 7,579 2.0

Aged 12 hr. at 740C Strain rate: 0.004 in/in/min 26 46,044 56,264 2.88300 40,879 46,154 14.32 500 30,769 36,044 10.26 700 6,484 7,363 4.28Aged 100 hr. at 750C Strain rate: 0.004 in/in/min 26 51,667 55,778 0.90300 45,536 47,946 13.43 500 32,571 38,857 9.28 700 7,091 7,364 4.28

The yield strength and tensile strength of the above plasma-consolidatedberyllium article, at room temperature, are much higher than the yieldstrength and tensile strength specifications for hot-pressed berylliumblocks which are 35,000 psi and 48,000 psi respectively.

EXAMPLE 11 A low oxygen grade of beryllium powder was plasmaconsolidatedwith arc-torch operating conditions as follows:

325 Tyler Mesh and finer Argon Argon-Hydrogen Powder Size Electrode GasPowder Carrier Gas Current 200 amperes Voltage 58 volts Torch Pressure34 psig Dispenser Pressure 37 psig Shield none Coating Time 5.5 hr.

Coating Thickness 1.225 in.

Powder Feed Rate Anode Type Torch Standoff 12.8 grams per minute CopperAnode 1.5 in.

The chemical analysis of the beryllium powder was as follows:

% Be 99.041 BeO 0.670 A1 0.047 c 0.050 Fe 0.09% Mg 0.042 s1 0.052

The geometry of this plated article was a thick-walled cylinder, 3.38inches inside dimaeter, 5.84 inches outside diameter, and 3.81 incheshigh. The coating substrate was an aluminum tube, prepared bygrit-blasting the bonding surface.

This beryllium article was heat treated in a special graphite enclosure.The enclosure was a cylindrical chamber, slightly larger than theberyllium object, and coated on all inside surfaces with BeO. Thisarrangement of enclosure and Be cylinder was evacuated to 10 mm Hgpressure, then heated at a rate of 4C/min. At 800C, the furnace wasbrought to a micron pressure of argon. At 1,200C, the temperature washeld constant for 4 hours. Cooling under argon pres sure was at a rateof l.7C/minute.

The oxygen content after sintering was found to be 1.7 percent as BeO,by neutron activation analysis. Density was measured by the waterdisplacement method to be 1.855 gm/cm, or 99.9 percent theoretical,corrected for BeO. The average linear intercept grain diameter was 18.3microns.

Samples were cut in various orientations from the sintered thick-walledcylinder for mechanical tests. First, compression test samples were cutwith the stress axis (1) parallel to the radial direction, (2) parallelto the cylinders length, and (3) parallel to a line tangent to thecylinder and perpendicular to the cylinders length. These samples werecarefully machined by surface grinding, then 0.002-0.003 inches wereremoved from each surface by chemical etching. The etchant had thecomposition:

17% HNO (concentrated) 82% Distilled water The results of roomtemperature compression tests as a function of sample orientation aregiven in Table 3. Testing was done on a Tinius-Olsen 20,000 lb. machine,measuring strain with a Tinius-Olsen deflectometer. The strain rate was0.010 inch/inch/minute. Treating the data with a two-sided t-test, themeasurement for yield stress at 0.2 percent strain was found to have nodistinguishable difference at a 95 percent level of confidence, for allthree orientations. This shows that isotropic mechanical properties arecharacteristic of this sintered plasma-consolidated beryllium article.

Tensile specimens were cut so that the stress axis would be in thecylinders longitudinal and tangential orientations. The samples wereflat sheets, ground to ASTM-E-8 specifications. These samples were agedin vacuum for 12 hours at 738C, then electropolished to remove0.002-0.003 inches from each surface. These tensile specimens weretested at various temperatures, from 25C to 650C. The testing apparatuswas a model TM lnstron operating at constant cross-head speed (strainrate equal to 0.004 inches/inch/minute at start of test). Strain wastaken from cross-head motion. Table 4 shows the results for the yieldstress at 0.2 percent strain, the ultimate tensile stress, and the totalplastic strain to fracture. These results show that substantially thesame tensile properties are obtained as a function of temperature forboth the tangential and longitudinal orientations.

Similar tensile specimens were prepared, except for the electropolishingstep, then aged in vacuum for various times at 600C and 740C. Thesamples were then electropolished to remove 0.002-0.003 inches persurface. The tensile strain rate was initially 0.004 inches-/inch/minute, and the corresponding cross-head speed was held constantthroughout the test. Table gives the complete tabulation of tensileproperties: yield strength, ultimate strength, and strain to fracture.The orientation factors for these samples were found to be under 0.16using the formula Compressive Strength as a Function of SpecimenOrientation Yield strength at 0.2% strain (psi) Mean yield strength and95% confidence limits (p Stress axis parallel to cylinder directionRadial r1756 Tangential 1'1523 Longitudinal 11157 TABLE 4 MechanicalProperties in Tension as a Function of Orientation and Temperature Aged12 Hours at 738C Orientation Temperature Yield stress Ultimate Plastictensile strain to stress fracture,

Longitudinal 25C 27,619 36,785 1.96 Tangential 25C 29,583 40,625 2.03Longitudinal 150C 25,217 35,652 6.28 Tangential 150C 25,052 34,947 5.40Longitudinal 260C 22.842 31,894 6.40 Tangential 260C 23,617 32,340 7.20Longitudinal 650C 9,677 10.107 4.45 Tangential 650C 10,625 10,833 4.40

TABLE 5 Elevated Temperature Tensile Properties Aged 100 Hours at 600CT, C YS (psi) 0.2 UTS (psi) 15;,

Aged 200 Hours at 600C 26 28,889 40,444 1.76 300 20,879 29,231 20.34 50018,587 24,674 17.51 700 6,044 7,143 2.86

Aged Hours at 740C 26 26,512 33,023 1.8 300 25,595 35,385 13.67 50018,072 30,602 10.98 700 7,692 7,802 2.78

TABLE 6 Orientation Factors for Sintered Plasma-Consolidated Berylliumof Example 11 Orientation Factor, 4 j 1, i=1 i=2 i=3 Theoretical Density=fim' b. heating said beryllium article in a substantial vacuum belowits sintering temperature at a rate less than about 10C per minute tosubstantially outgas and thermally desorb the gases and condensed gasesoccupying the pores and pore surfaces, respectively',

c. sintering said outgassed beryllium article at a temperature betweenabout 1,l80C and about l,250C for a period between about 15 minutes.

Theoretical Density= 7 9 %BeO b. heating said beryllium article in asubstantial vacuum below its sintering temperature at a rate less thanabout 10C per minute to substantially outgas and thermally desorb thegases and condensed gases occupying the pores and pore surfaces,respectively;

c. sintering said outgassed beryllium article at a temperature betweenabout 1,180C and about l,250C for a period between about minutes andabout 6 hours so as to increase the density of said article to greaterthan 99 percent of theoretical; and

d. cooling said densified article to a temperature between about 500Cand about 750C and holding thereat for a period of at least 10 hours.

3. The process as in claim 1 wherein in step b said beryllium article isheated below its sintering temperature at a rate about 4C per minute; instep c said outgassed beryllium article is sintered between about 1,190Cand about l,2l0C for a period between about 3 hours and 4 hours; and instep d said densified article is cooled at a rate between about 15C andabout C per minute.

4. The process as in claim 1 wherein step a said beryllium article has aBeO content of less than 6 percent by weight.

5. The process as in claim 1 wherein in step a said beryllium articlehas a BeO content of less than 2.5 percent by weight.

6. The process as in claim 3 wherein in step a said beryllium articlehas a BeO content of less than 6 percent by weight.

7. The process as in claim 3 wherein in step a said beryllium articlehas a BeO content of less than 2.5 percent by weight.

8. The process as in claim 3 wherein after step d the following step isadded:

e. subjecting said densified article to an additional heat treatment ata temperature of between about 500C and about 750for a period of betweenabout 10 hours and about 100 hours.

9. A process for making a highly densified plasmaconsolidated berylliumarticle comprising the steps:

a. preparing a plasma-deposited beryllium article from beryllium powdercontaining a minor amount of impurities, said plasma-deposited articlehaving a theoretical density greater than percent based on percenttheoretical density corrected for BeO content according to the formula:

b. heating said beryllium article in a substantial vacuum below itssintering temperature for a time period sufficient to decrease theas-coated absorbed gas level of the article to below 10" moles per cubiccentimeter of porosity;

c. sintering said outgassed beryllium article at a temperature betweenabout 1,180C and about l,250C for a period between about 15 minutes andabout 6 hours so as to increase the density of said article to greaterthan 99 percent of theoretical; and

d. cooling said densified article to ambient at a rate between 1C andabout 10C per minute.

10. A process for making a highly densified plasmaconsolidated berylliumarticle comprising the steps:

a. preparing a plasma-deposited beryllium article from beryllium powdercontaining a minor amount of impurities, said plasma-deposited articlehaving a theoretical density greater than 85 percent based on 100percent theoretical density corrected for BeO content according to theformula:

100 BeO Theoretical Density= (7 7 B60 between about 1C and about 10C perminute.

2. A process for making a highly densified plasma-consolidated beryllium article comprising the steps: a. preparing a plasma-deposited beryllium article from beryllium powder containing a minor amount of impurities, said plasma-deposited article having a theoretical density greater than 85 percent based on 100 percent theoretical density corrected for BeO content according to the formula:
 3. The process as in claim 1 wherein in step b said beryllium article is heated below its sintering temperature at a rate about 4*C per minute; in step c said outgassed beryllium article is sintered between about 1,190*C and about 1,210*C for a period between about 3 hours and 4 hours; and in step d said densified article is cooled at a rate between about 1.5*C and about 2.0*C per minute.
 4. The process as in claim 1 wherein step a said beryllium article has a BeO content of less than 6 percent by weight.
 5. The process as in claim 1 wherein in step a said beryllium article has a BeO content of less than 2.5 percent by weight.
 6. The process as in claim 3 wherein in step a said beryllium article has a BeO content of less than 6 percent by weight.
 7. The process as in claim 3 wherein in step a said beryllium article has a BeO content of less than 2.5 percent by weight.
 8. The process as in claim 3 wherein after step d the following step is added: e. subjecting said densified article to an additional heat treatment at a temperature of between about 500*C and about 750*for a period of between about 10 hours and about 100 hours.
 9. A process for making a highly densified plasma-consolidated beryllium article comprising the steps: a. preparing a plasma-deposited beryllium article from beryllium powder containing a minor amount of impurities, said plasma-deposited article having a theoretical density greater than 85 percent based on 100 percent theoretical density corrected for BeO content according to the formula:
 10. A process for making a highly densified plasma-consolidated beryllium article comprising the steps: a. preparing a plasma-deposited beryllium article from beryllium powder containing a minor amount of impurities, said plasma-deposited article having a theoretical density greater than 85 percent based on 100 percent theoretical density corrected for BeO content according to the formula: 